A new study seems to offer even more evidence on why pregnant women should get the flu vaccine. Researchers think that prenatal exposure to the flu might increase a baby's chances of developing bipolar disorder later in life.

The study, published recently in JAMA Psychiatry, looked at the link between a pregnant mother's flu exposure and her child's future chances of being diagnosed with bipolar disorder. Researchers found that children exposed to the flu during pregnancy may have almost four times the risk of later developing bipolar disorder.

Researchers used data from a study that involved pregnant mothers living in Alameda County, California, between 1959 and 1966. Using the mothers' medical records and medical data for their children, researchers compared the information for 92 kids who were exposed to the flu while in the womb, and on 722 who were not.

Of the children exposed to the flu, about 9 percent were later diagnosed with bipolar disorder compared to about 3 percent of the kids who were not exposed.

"Maternal influenza is related to bipolar disorder," said Dr. Alan Brown, a professor of psychiatry and epidemiology at Columbia University in an interview with Reuters Health. When asked how prenatal flu exposure could be linked to a child's bipolar risk, Brown responded, "[w]e think there is an inflammation going on in the fetus due to this infection and it can alter key aspects of brain development and function."

Previous studies had already established a link between prenatal flu exposure and a child's risk of developing other mental health disorders, namely schizophrenia.

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